Revolving doors are known and have been used extensively to provide a substantially weather resistant simultaneous ingress and egress facility in many modern buildings. Revolving doors are particularly well suited to prevent excessive energy losses that may arise from conventional doors, when it is either much hotter or much colder on one side of the door than on the other, because of the limited amount of air that may pass through the doorway of a revolving door.
Generally, the side walls of revolving doors are curved, and subtend an arc of slightly greater than 90.degree.. The door leaves are usually supported from a central axle, at 90.degree. to each other. The preferred alignment for the door, when not in use, is for two door leaves to be adjacent each side wall, which is commonly referred to as a quarter point alignment. With the quarter point alignment two weather seals are formed between the inside and outside of the building, and additionally, the doorway has a pleasing open look when approached by a person wanting to pass through the doorway.
There are essentially two types of revolving doors: those that have a power drive to assist in the rotation of the door, such as an electric motor, and those that are manually operated. In the manually operated revolving doors the rotating force for the door is provided by the person who seeks to pass through the doorway.
This invention relates to manually driven revolving doors, and in particular to a return mechanism for ensuring that when the door is not in use, the door leaves of the revolving door are aligned in the most efficient and aesthetic manner. Alignment mechanisms have been known and are used in association with power driven revolving doors, such as the devices shown in U.S. Pat No. 3,497,997, entitled QUARTERLINE STOP CONTROL SYSTEM FOR POWER DRIVEN REVOLVING DOORS.
Essentially the device of this prior patent, and other inventions of this type, operate in the following manner. Upon the revolving door being displaced from its resting position, for example by a person wishing to pass through the doorway, a switch is triggered activating an electric motor. The electric motor then rotates the door at a preselected speed. After a preselected amount of rotation, further switching occurs which can cause the door to slow down, and eventually stop with the door leaves at any desired location.
However, there are a number of undesirable limitations of the invention disclosed in this United States patent, and in these types of devices in general. Firstly, they require the use of a powerful electric motor able to accelerate the door to the preselected speed almost instantaneously. Also, because of the space constraints of the door frame it is often necessary to use a large number of heavy gauge interlocking gears to transmit the drive from the motor to the central axle of the door. Both of these requirements add considerably to the expense of the revolving door, and to the difficulty of manufacturing, installing and maintaining the door.